[PATCH V4 10/27] ublk: handle UBLK_U_IO_PREP_IO_CMDS

Ming Lei
2025-11-21T01:59:52Z

This commit implements the handling of the UBLK_U_IO_PREP_IO_CMDS command,
which allows userspace to prepare a batch of I/O requests.

The core of this change is the `ublk_walk_cmd_buf` function, which iterates
over the elements in the uring_cmd fixed buffer. For each element, it parses
the I/O details, finds the corresponding `ublk_io` structure, and prepares it
for future dispatch.

Add per-io lock for protecting concurrent delivery and committing.

Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
drivers/block/ublk_drv.c | 193 +++++++++++++++++++++++++++++++++-
include/uapi/linux/ublk_cmd.h | 5 +
2 files changed, 197 insertions(+), 1 deletion(-)

diff --git a/drivers/block/ublk_drv.c b/drivers/block/ublk_drv.c
index 21890947ceec..66c77daae955 100644
--- a/drivers/block/ublk_drv.c
+++ b/drivers/block/ublk_drv.c
@@ -117,6 +117,7 @@ struct ublk_batch_io_data {
struct ublk_device *ub;
struct io_uring_cmd *cmd;
struct ublk_batch_io header;
+ unsigned int issue_flags;
};

/*
@@ -201,6 +202,7 @@ struct ublk_io {
unsigned task_registered_buffers;

void *buf_ctx_handle;
+ spinlock_t lock;
} ____cacheline_aligned_in_smp;

struct ublk_queue {
@@ -270,6 +272,16 @@ static inline bool ublk_dev_support_batch_io(const struct ublk_device *ub)
return false;
}

+static inline void ublk_io_lock(struct ublk_io *io)
+{
+ spin_lock(&io->lock);
+}
+
+static inline void ublk_io_unlock(struct ublk_io *io)
+{
+ spin_unlock(&io->lock);
+}
+
static inline struct ublksrv_io_desc *
ublk_get_iod(const struct ublk_queue *ubq, unsigned tag)
{
@@ -2531,6 +2543,171 @@ static int ublk_ch_uring_cmd(struct io_uring_cmd *cmd, unsigned int issue_flags)
return ublk_ch_uring_cmd_local(cmd, issue_flags);
}

+static inline __u64 ublk_batch_buf_addr(const struct ublk_batch_io *uc,
+ const struct ublk_elem_header *elem)
+{
+ const void *buf = elem;
+
+ if (uc->flags & UBLK_BATCH_F_HAS_BUF_ADDR)
+ return *(__u64 *)(buf + sizeof(*elem));
+ return 0;
+}
+
+static struct ublk_auto_buf_reg
+ublk_batch_auto_buf_reg(const struct ublk_batch_io *uc,
+ const struct ublk_elem_header *elem)
+{
+ struct ublk_auto_buf_reg reg = {
+ .index = elem->buf_index,
+ .flags = (uc->flags & UBLK_BATCH_F_AUTO_BUF_REG_FALLBACK) ?
+ UBLK_AUTO_BUF_REG_FALLBACK : 0,
+ };
+
+ return reg;
+}
+
+/*
+ * 48 can hold any type of buffer element(8, 16 and 24 bytes) because
+ * it is the least common multiple(LCM) of 8, 16 and 24
+ */
+#define UBLK_CMD_BATCH_TMP_BUF_SZ (48 * 10)
+struct ublk_batch_io_iter {
+ void __user *uaddr;
+ unsigned done, total;
+ unsigned char elem_bytes;
+ /* copy to this buffer from user space */
+ unsigned char buf[UBLK_CMD_BATCH_TMP_BUF_SZ];
+};
+
+static inline int
+__ublk_walk_cmd_buf(struct ublk_queue *ubq,
+ struct ublk_batch_io_iter *iter,
+ const struct ublk_batch_io_data *data,
+ unsigned bytes,
+ int (*cb)(struct ublk_queue *q,
+ const struct ublk_batch_io_data *data,
+ const struct ublk_elem_header *elem))
+{
+ unsigned int i;
+ int ret = 0;
+
+ for (i = 0; i < bytes; i += iter->elem_bytes) {
+ const struct ublk_elem_header *elem =
+ (const struct ublk_elem_header *)&iter->buf[i];
+
+ if (unlikely(elem->tag >= data->ub->dev_info.queue_depth)) {
+ ret = -EINVAL;
+ break;
+ }
+
+ ret = cb(ubq, data, elem);
+ if (unlikely(ret))
+ break;
+ }
+
+ iter->done += i;
+ return ret;
+}
+
+static int ublk_walk_cmd_buf(struct ublk_batch_io_iter *iter,
+ const struct ublk_batch_io_data *data,
+ int (*cb)(struct ublk_queue *q,
+ const struct ublk_batch_io_data *data,
+ const struct ublk_elem_header *elem))
+{
+ struct ublk_queue *ubq = ublk_get_queue(data->ub, data->header.q_id);
+ int ret = 0;
+
+ while (iter->done < iter->total) {
+ unsigned int len = min(sizeof(iter->buf), iter->total - iter->done);
+
+ if (copy_from_user(iter->buf, iter->uaddr + iter->done, len)) {
+ pr_warn("ublk%d: read batch cmd buffer failed\n",
+ data->ub->dev_info.dev_id);
+ return -EFAULT;
+ }
+
+ ret = __ublk_walk_cmd_buf(ubq, iter, data, len, cb);
+ if (ret)
+ return ret;
+ }
+ return 0;
+}
+
+static int ublk_batch_unprep_io(struct ublk_queue *ubq,
+ const struct ublk_batch_io_data *data,
+ const struct ublk_elem_header *elem)
+{
+ struct ublk_io *io = &ubq->ios[elem->tag];
+
+ data->ub->nr_io_ready--;
+ ublk_io_lock(io);
+ io->flags = 0;
+ ublk_io_unlock(io);
+ return 0;
+}
+
+static void ublk_batch_revert_prep_cmd(struct ublk_batch_io_iter *iter,
+ const struct ublk_batch_io_data *data)
+{
+ int ret;
+
+ /* Re-process only what we've already processed, starting from beginning */
+ iter->total = iter->done;
+ iter->done = 0;
+
+ ret = ublk_walk_cmd_buf(iter, data, ublk_batch_unprep_io);
+ WARN_ON_ONCE(ret);
+}
+
+static int ublk_batch_prep_io(struct ublk_queue *ubq,
+ const struct ublk_batch_io_data *data,
+ const struct ublk_elem_header *elem)
+{
+ struct ublk_io *io = &ubq->ios[elem->tag];
+ const struct ublk_batch_io *uc = &data->header;
+ union ublk_io_buf buf = { 0 };
+ int ret;
+
+ if (ublk_dev_support_auto_buf_reg(data->ub))
+ buf.auto_reg = ublk_batch_auto_buf_reg(uc, elem);
+ else if (ublk_dev_need_map_io(data->ub)) {
+ buf.addr = ublk_batch_buf_addr(uc, elem);
+
+ ret = ublk_check_fetch_buf(data->ub, buf.addr);
+ if (ret)
+ return ret;
+ }
+
+ ublk_io_lock(io);
+ ret = __ublk_fetch(data->cmd, data->ub, io);
+ if (!ret)
+ io->buf = buf;
+ ublk_io_unlock(io);
+
+ return ret;
+}
+
+static int ublk_handle_batch_prep_cmd(const struct ublk_batch_io_data *data)
+{
+ const struct ublk_batch_io *uc = &data->header;
+ struct io_uring_cmd *cmd = data->cmd;
+ struct ublk_batch_io_iter iter = {
+ .uaddr = u64_to_user_ptr(READ_ONCE(cmd->sqe->addr)),
+ .total = uc->nr_elem * uc->elem_bytes,
+ .elem_bytes = uc->elem_bytes,
+ };
+ int ret;
+
+ mutex_lock(&data->ub->mutex);
+ ret = ublk_walk_cmd_buf(&iter, data, ublk_batch_prep_io);
+
+ if (ret && iter.done)
+ ublk_batch_revert_prep_cmd(&iter, data);
+ mutex_unlock(&data->ub->mutex);
+ return ret;
+}
+
static int ublk_check_batch_cmd_flags(const struct ublk_batch_io *uc)
{
unsigned elem_bytes = sizeof(struct ublk_elem_header);
@@ -2587,6 +2764,7 @@ static int ublk_ch_batch_io_uring_cmd(struct io_uring_cmd *cmd,
.nr_elem = READ_ONCE(uc->nr_elem),
.elem_bytes = READ_ONCE(uc->elem_bytes),
},
+ .issue_flags = issue_flags,
};
u32 cmd_op = cmd->cmd_op;
int ret = -EINVAL;
@@ -2596,6 +2774,11 @@ static int ublk_ch_batch_io_uring_cmd(struct io_uring_cmd *cmd,

switch (cmd_op) {
case UBLK_U_IO_PREP_IO_CMDS:
+ ret = ublk_check_batch_cmd(&data);
+ if (ret)
+ goto out;
+ ret = ublk_handle_batch_prep_cmd(&data);
+ break;
case UBLK_U_IO_COMMIT_IO_CMDS:
ret = ublk_check_batch_cmd(&data);
if (ret)
@@ -2770,7 +2953,7 @@ static int ublk_init_queue(struct ublk_device *ub, int q_id)
struct ublk_queue *ubq;
struct page *page;
int numa_node;
- int size;
+ int size, i;

/* Determine NUMA node based on queue's CPU affinity */
numa_node = ublk_get_queue_numa_node(ub, q_id);
@@ -2795,6 +2978,9 @@ static int ublk_init_queue(struct ublk_device *ub, int q_id)
}
ubq->io_cmd_buf = page_address(page);

+ for (i = 0; i < ubq->q_depth; i++)
+ spin_lock_init(&ubq->ios[i].lock);
+
ub->queues[q_id] = ubq;
ubq->dev = ub;
return 0;
@@ -3021,6 +3207,11 @@ static int ublk_ctrl_start_dev(struct ublk_device *ub,
return -EINVAL;

mutex_lock(&ub->mutex);
+ /* device may become not ready in case of F_BATCH */
+ if (!ublk_dev_ready(ub)) {
+ ret = -EINVAL;
+ goto out_unlock;
+ }
if (ub->dev_info.state == UBLK_S_DEV_LIVE ||
test_bit(UB_STATE_USED, &ub->state)) {
ret = -EEXIST;
diff --git a/include/uapi/linux/ublk_cmd.h b/include/uapi/linux/ublk_cmd.h
index 2ce5a496b622..c96c299057c3 100644
--- a/include/uapi/linux/ublk_cmd.h
+++ b/include/uapi/linux/ublk_cmd.h
@@ -102,6 +102,11 @@
_IOWR('u', 0x23, struct ublksrv_io_cmd)
#define UBLK_U_IO_UNREGISTER_IO_BUF \
_IOWR('u', 0x24, struct ublksrv_io_cmd)
+
+/*
+ * return 0 if the command is run successfully, otherwise failure code
+ * is returned
+ */
#define UBLK_U_IO_PREP_IO_CMDS \
_IOWR('u', 0x25, struct ublk_batch_io)
#define UBLK_U_IO_COMMIT_IO_CMDS \
--
2.47.0